Machine tool



Dec. 22, 1959 K. F. LlERsE 2,917,874

MACHINE TOOL INVENTOR.

KURT F. LIERSE AT TO RN EYS K. F. LIERSE MACHINE A'I'OOL Dec. 22, 1959 3 Sheets-Sheet 2 Filed Aug. 25 1958 oF T om INVENTOR. KU RT F. LIERS E ATTO RNYS v @mmm K. F. LlERsE 2,917,874

MACHINE ,TooL

3 Sheets-Sheet 3 Dec. 22, 1959 Filed Aug.,25, .1958

AT TO R N EYS in the machine tool shown in Figure 1 to effect Y reciprocation of each of the tables; and

United States Patent O MACHINE 'rooL A Kurt `F. Lierse, Harrisburg, Pa., assignor to Thompson vRamo Wooldridge Inc., a corporation of Ohio This invention relates generally to machine tools, and more specifically 'to a machine tool, such as a surface grinder, having a pair of workpiece 'supporting tables incorporated therein. v c

.Although the Aprinciples ofthe present invention may be included in various machine tools, a particularly useful application is made in surface grinders. In particular, when a' conventional grinder is used, its table is loaded with production parts, which are then roughground to within a few thousandths of the desired dimension. Thereafter the wheel is'dressed and the parts are linish ground. They are then unloaded and checked after which the table is reloaded and the foregoing procedure repeated. It is inherent in this type of operation that the machine will be idle during loading, unloading vand part checking. It is also apparent that the opera- Ytor will be idle during rough grinding, wheel dressing,

vrandiinishv grinding.

The present inventionY `contemplates the Yutilization of '"two tables Vpreferablysupported on the same ways, only one ofiyvhichetablesmay'be operated at a'given'time Withvthi's machine,l all unloading, checking andV reloading of one'table is accomplished while the other Vtableis grinding parts. Thus bothk the machinegand the operator may bekept busy substantially all vof the time.

fr Accordiiiglyf,` it is an-object ofthe present invention Ato provide an improved machineV tool having a'pair of alternatively usable tables incorporated therein. -A Anothero'bje'ct ofthe present 'invention is to provide an improved surface grinder.

Yet another object of the present invention is to provide a machine tool having a hydraulic system capable of independently controlling each of a pair of workpieceV supporting tables. Y y

l Another object of the present invention is to' provide an electric `control circuit for a machine tool having a pair of hydraulically operated tables.

Yet another'object of this lnvention is the provision` of controls for a machine tool having a pair of workpiece supporting tables.

-Many other advantages, features and additional objects ofthe present invention'will` become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown byway of illustrative example.

On the drawings:

. Figure 1 is a front elevational view of 'a surface grinder equipped with a pair of workpiece supporting tables provided-in accordance with the principles of the present invention;

Figure 2 is a diagram of the hydraulic system used proper Figure 3 is a diagram ofthe electrical circuit employed to control the hydraulic system shown in Figure 2.

Asshown onthe drawings:

2,917,874 Patentedy Dec. 22, 1959 ICC The principles of this invention are particularly useful when embodied in a surface grinder such as illustrated in Figure 1, generally indicated by the numeral 10. While the instant invention has been disclosed in connection with a grinder, it is to be understood that machine tools employing various types of shaping or cutting tools may be provided with my invention.V The machine tool or surface grinder 10 includes a base 11, a toolsupporting assembly or member 12, which in this example is provided with a grinding wheel 13, andY a pair of tables for supporting workpieces including a left table I14 and a right table 15. Each ofthe tables V14 and 15 is reciprocably supported by the base adjacent to the tool supporting member 12 whereby the grinding wheel 13 may engage workpieces supported on the tables-14 and 15. In this example, the right hand table 15 lhas been made slightly longer than the left hand table so as to enable it to support a wheel dresser mechanism generally indicated by the numeral 16. f

A reversible driving means is Yprovided for each of the tables 14, 15 whereby either table may berreciprocated only when the other table is in a fully retracted position.

'The reciprocation takes place automatically,'and the operator is provided with controls whereby he may select which of the tables 14, 15 is to be reciprocated. To this end, there is provided a iiuid system, such as a hydraulic system, for driving the tables, together with an electrical system for controlling the liuid system. The operators control stations form a part of the electrical system which operates to position a plurality of valves jointlyso that only the selected table'can be reciprocated.

,Referring now to Figure 2, there is shown thedetails of the hydraulic system generally indicated at 17, and provided with a rudimentary group'ot` electrical controls for operating one of the tables.

The fluid driving system 17 includes a source of pressurized uid here comprising a hydraulic pump 18 driven by an electric motor 19 which draws hydraulic fluid from a reservoir or tank 20. v

The pump 18 dischargesl through a hydraulic `reief valve 21 to a line 22 which supplies fluid to anautomatic down feed system 23 for the grinding wheel 13,

which system. is of conventional construction, and also to a fluid control means here comprising a master valve 24. The master valve 24 is of conventional construction and includes a main spool (not shown) which is under the control of a pilot valve 25 which receives hydraulic liuid from a line 26 to position the main spool. The position of the pilot valve 25 is governed by a table reverse lever 27 which is pivotally supported by` the master valve 24 and which has an upper end 28 adapted to engage a plurality of dogs 29-32 on the tables 14 and 15; When the table reverse lever 2,7 is in one position, the port 33 discharges hydraulic fluid underpressure while the port 34 is simultaneously in communication with the return line 35 leading to theV tank 20. When the table reverse lever 27 is in the opposite position, the port 34 is supplied with hydraulic iiuid under pressure while the port 33 communicates with the hydaulic return line 35. n

The master valve 24 is also provided with a discharge port 36 which communicates with a hydraulically operated cross feed 37 which is mechanically connected to the grinding wheel 13. The details of the cross feed 37 are known in the art and do not form a part of the instant invention. The master valve 24 isy provided with a lever 33 by which the cross feed 37. may be turned on or o. Y Y

While the lever 27 is used to effect automatic reversal or reciprocation of a selected table, a further lever 39.is provided, the position of which is` eiectiveto'startv `or stop table reciprocation. When, for example, theright hand table is disposed adjacent to the grinding wheel 13, the upper end 28 of the lever 27 is disposed between the dogs 31 and 32. When the lever 27 is positioned toward the right, the dog 32 strikes the upper end thereof v28 causing the lever 27 to move to the left. This in Vturn effects a pressure reversal at kthe ports 33 and 34 whereby the table 15 is ,caused to move to the right until the dog 31 strikes and moves the upper en d 28 of the lever 27 toward the right which again effects table movement in the opposite direction. Thus the master valve 24 comprises means which is responsive to the table movement in either direction and which is operative to automatically efect periodic reversal of the table movements.

A Huid motor -or actuator 40 is provided with a piston i rod 41 to which there is connected a piston rod 42 which has a driving connection as at 43 with the right table 15.' A second uid actuator or motor 44 has a piston 45 to which is connected a piston rod 46 which has a driving connection as at 47 with the lefthand table` 14.

Operatively intermediate the masterV valve 24 and the duid-motors 40 and 44, there is provided a first electric selector valve 48 and a second electric selector valve 49. VIt will be noted that veach of the valves 48 and 49 in this knembodiment are individually intermediate the master .valveor control means 24 and both of the motors 40 and .4.4. Thus the port 33 of the master valve 24 communicates with a pressure port 50 on the selector valve 48, while the pressure port 34 communicates with a pressure `port 51.on the selector valve 49. vThe valves 48 and 49 'areeach respectively provided with la return port 52 and vSla-which communicates with the tank 20. lThe valve 48 is providedwithfa port 54 which communicates with the .-rod or left .end of the motor 44 and a port 56 ,which communicates with the left or head end of the motor 40. Similarly, the valve 49 is provided with a port 55 whichcommunicates with vthe right or head end of the ;motor 44, and a port 57 which communicatesv with the right or rod end of the motor .48. VThe .valves 48, y49 are each electrically actuated and hydraulically operated, and comprise conventional construction. To this end, the pilot pressure line 26 also communicates with each of the valves 48, 49, and solenoids Sii-61 are provided for actuating the pilot valve portions thereof respectively.

-Typical valves employed may also include drain ports by which internal leakage is conducted to the tank 20. For purposes of clarity, all drain ports and drain lines offthis type have been omitted from the drawing, the provision of them-for components requiring the same being conventional.

Themaster valve 24 is also provided with an additionalport which communicates with a combined retard and lubrication system 62 of a type known in the art.

The surface'grinder 10 disclosed herein has also been providedwith a coolant pump 63 which draws coolant from-a tank 64, sending it through a check valve 65 to a'y pair of solenoid valves 66, 67, each of which is respectivelyprovided with a line 68, 69 communicating with the table 14 and the table 15. Suitable `means are pro- `vided for returning the used coolant to the tank 64, but

are Vnot shown in the drawing. When the valves 66 and 67 are de-energized, no coolant can ow therethrough.

Figure 2 also includes a simplified wiring diagram by which the right hand table 15 may be operated. A source of power is connected to a manually operable selector switch 70 which is shown to have three positions, one for selecting operation of the left hand table 14, a middle ofi position and a Vthird position where the circuit'for the right hand table is energized. The circuit extends from the selector switch 79 to a limit switch 71 which is normally open. However, when the left hand table 14 is in a fully retracted position, a stop plate 72 engages the switch 71 to hold it electrically The relay 74 includes a pair of normally open contacts 75, one of which is connected to the source of power and the other of which is connected to the valve solenoids 59, 61, and the solenoid of the coolant valve 67. When the relay 74 is thus energized, the closing of the contacts 75 provides power to the above indicated solenoids.

When the solenoids 59 and 61 are energized, the left hand end of the motor 44 and the port 54 of the valve 48 are in communication with `the vreturn line 52, while the right hand end of the motor 44 and the port 55 are in communication with the return line 53. Simultaneously, the port 50 of the valve 48 is in communication with the port 56 and the left hand end of the motor 40 while the port 51 of the valve 49 is in communication with the port 57 thereof and the right end of the motor 40. With the circuit for the right table 15 thus energized, the lever 27 may be manually positioned toward the right to cause the right `table to move toward the left. Moving the lever 27 to the right permits uid under pressure to discharge through the port 34 ,of the master valve 24 through the port 51 andthe port57 of the valve 49 and into the rod end of the motor .40, `thereby causing movement to the left. Fluid on the-left side of the piston 41 leaves through the left end of the motor 40 and enters the port 56 ofthe valve 49 and is discharged through the port 50 to enter l,the master lvalve 24 at the port 33 and to be discharged therefrom through the return line 35 `to the tank 20. When V,the table reverse lever 27 is engaged by the dog 32 it moves to the left to reverse the pressure at the ports 33 and 34 of the master valve 24 therebycausing fluid to iiow through the same circuit and the same ports in theopposit'e direction, and likewise discharging throughrthe line 35.to the tank'20. Y'

It is to be noted that the solenoid valve 67 is connected electrically across thesolenoids59 and 61, Aor in parallel therewith, whereby the ysolenoid 67 is ienergized' only when the right hand table is to 'be-reciprocated.' Thus an interruption of the control circuitforthe right `hand tablev also interrupts the flow of coolant thereto.

The control circuit for the'left hand table, although not shown in the-drawing, is similar to the right hand table circuit, and extends through a limit switch i'76.which is-engageable by a stop plate 77 `carriedby 1the `right table 15. The valve solenoids 58 and k6,0 together with the solenoid yvalve 66 are similarly simultaneously energized to effect operation of the lefttable 14.` Because of the structure of the ,selector switch70, the left table can be energized only when the right table controls are de-energized, and when theright table is ina retracted position whereby the limit switch 76 is held ina closed position. n

When the controls are energized to operatekthe left table, the left end of the right motor 1,40 communicates through the port 56 and the port 52 of the valve 48 with the tank 2i), while theright end of the .right vmotorr46 communicates through the ports 57 and 55, with thetank 20. The left or rod end of the motor,44 communicates through the port 54 with the port 50 of the valve 48 and the port 33 of the master `valve 24, whilev the right end of the left motorcommunicates with the port 55 and the port 51 of the valvei49 and the pressure port 34 of the master valve 24. To move the left tablertotheright, the table reversing lever 27 is moved yto the left, thereby discharging pressure at the port 33 which passes through the ports 50 and 54 of the valve 48 tothe left endV of the motor 44. Fluid in the motor 44 totheright of the piston. 45 is returned through the ports .S5/and. theport 51 of the valve 49 to the port 35 and ythence through the return line 35 to the tank 20.

This movement continues until the dog 29Y engages-the upper end 28 of the table reverse lever.27, moving it to the right, which effects areversal of pressure at theoutlets -33 and 341of the master valve-,24. Thus.pres sure is discharged at the port 34 andpasses through-the. ports 51 and 55 of the valveY 49 to the right end of the motor 44 to cause the table 14 to move to the left. Fluid to the left of the piston 45 is returned through the ports 54 table is instantly interrupted whereby reciprocation would immediately terminate. Moreover, reciprocation cannot initiate unless-the opposite table is fully retracted.

- The check valve 65 on the discharge side of the coolant i pump 63 prevents a draining of the coolant lines whenever the pump 63 is stopped. Y

. Adjacent to the upper endV 28 of the table reverse lever 27 there is provided a retard switch 78 which is engageable by the stop plate72 in the event that the dog 29 should overrun the upper end of the lever 28. The switch 78 communicates with the retard and lubrication system to etect diversion of the reciprocation-etfecting uid at ahigh rate of ow.

Thus the switch 78 may be energized by the combined stop and overrun plate 72 to prevent the left table 14 from vstriking the right table 15. The right table has been. provided with a separate overrun plate 79 for also engaging the retardswitch 78 in the event that the dog 32 overruns the upper end 28 of the lever 27. This plate thus prevents the right, hand table 15 from striking the kleft table 14. y A

' Referring now to Figure 1, the combined overrun and stop plate 72 is shown as being secured to the left table 14 in an adjustable manner. The dogs 29-32 are likewise also secured toone of the tables 14 and 15. The .stop plate 77 and the overrun plate 79 are shown to comprise separate plates whereby the relative point at which the. overrun plate 79 engages the retard switch 78 may be adjusted without affecting the point at which the stop plate 77 engages the limit switch 76. It is to be understood .that the overrun and stop plate functions may be 6 supply vfurtherrcommunicates with the elevation controls and circuits generally indicatedv at 86. Still further, the lines 81-83 communicate with each of a hydraulic pump relay 87 and a coolant pump relay 88. A coolant pump motor 89 connected to the coolant pump 63 of Figure 2, is shown to comprise a three phase motor connected to the opposite contacts as are the lines 81-83 so that when the relay 88 is closed, the motor is energized. Intermediate the coolant pump relay 88 and the coolant pump 89,' there is provided a pair of safety relays 90 and 91, the coils of which are each connected in series with one of the lines leading to the coolant pump motor 89. The controls for the coolant pump motor 89 are energized from a step down transformer 92 which has a primary connected across the lines 81 and 82. Each of the legs of the secondary thereof passes through a fuse v93 and 94 respectively. The fuse 93 is connected to variouscontrols, while the return lines therefrom have all been omitted to simplify the drawing, the return line being indicated by the various points denoted as "x which are connected to the fuse 94. Thus the fuse 93 has a downwardly extending control 'power line 95 which communicates with the stop switch 96 and the start switch 97 forv the coolant pump motor 89. The opposite contact of the start switch 97, which is a normally open momentary switch, is connected to the coil of coolant pump relay 88. Thus when the start switch is depressed,

Va circuit is closed to the coil of the relay 88 which causes the contacts thereof to close. Three of the pairs of contacts bring power to the coolant pump motor as described and thereby also energize the coils of the safety relays 90 and-91. Thus with the relay 88 closed, the

relays 90 `and 91 closed, there Yis provided an alternate combined as shown for the left hand table or may be separated as shown for the right hand table.

The dogs 30 and 31 are not only secured to the tables 14 and 15, but are looselyfpivotally mounted thereon so that each may pivot out of the way past the upper end 28 of the lever 27, as the respective tables are being Ymoved to an operative position with 'respect to the grinding wheel 13. It'desired, a small handle` may be Yprovided as at 30a and 31a for manually pivoting the dogs 30 and 31 respectively. r

.-As bestseen in Figure'2, a double purpose downfeed and lubrication switch 80 is provided adjacent to the upper end of the table reverse lever 27. (This switch is obscured by the lever itself in Figure l.) Theswitch 80 communicates electrically withthe automatic downfeed system 23 and with-the lubrication ,system 62 for automatically providing an increment of downfeed of the 4wheel '13 andv lubricationof `the table supports foreach stroke of each tableand in synchronism therewith. vThus "the-downfeeding and lubrication both terminate when ^reciprocation of either table is terminated.`

Referring now toFigure 3, there 1s `showna complete control circuit for both of the tables 14Y and 15. It is vto Y'be/understood that this figure" represents a preferred circuit for the control of the hydraulic tables, and that less rei-'med circuits such asV shown in Figure 2 may yalso be employed to advantage. Q j

` Athree phase power supply including lines 81, 82 and 83 communicates with the motor for the grinding wheel,

'and its control circuit, generally indicated at 84. The power supply also communicates with the dresser and its control'circuit generally indicated at- 85. Thepower stop `ing circuit extending lthrough the stop switch 96, by

the momentary actuation of which the relay 88 andthe pump motor 89 may be de-energized. In the event that current in one of two phases should fail, one of the relays 90 and 91 will open to stop the pump motor 89.

kThe details of the circuit used to operate the cool-ant pump motor 89 are known inthe art and do not form a ypart of this invention.

The hydraulic pump motor 19 is provided with a substantially yidentical set of controls which includes the hydraulic pump relay 87, a pair of safety relays 9S, 99, :a normally open momentary start switch 100, and a normally closed momentary stop switch 101. Power for the motor 19 is brought from the lines 81w-83 to the relay-87, which, upon closing, brings the power to the hydraulic'pump motor 19, two of the lines including the coils of the relays--98 and 99 in series. Control power'is brought from the line 95 to each of the start and stop switches 100 and 101 respectively, whereby 'closing of thenswitch 100 momentarily closes the relay Y 87 to not only bring power to the motor 19, but to close the`holding circuit for the current passing through the coil of the relay 87. -As in the case of the coolant pump A second control power line 101a communicates with the fuse 93 to bring control power to each of the downyfeed controls 102, the lubrication controls 103, and the retard controls 104, each of which controls are provided 'with sub-circuits known in the art. The dual purpose downfeed and lubrication switch communicates with Veach of the downfeed controls 102 and the lubrication controls 103, while the retard switch 78 communicates with the retard controls 104.

that `is connected across or in parallel with the coil of the hydraulic pump relay 87, and is thereby under the control of the start switch 100 and the stop switch 101 for the hydraulic pump motor. Thus the coil 106 of the relay 105 `operates in coordination with the hydraulic. pump motor 19. The control power line 95 is connected to the contacts 107 of the relay 105 through which all electric power for the electric control circuit for the reciprocating tables is provided. The power circuit thus extends from the fuse 93 through the line 95, and the contacts 107, to a normally closed momentary stopswitch S which in turn is connected to the selector switch 70. The selector switch 70 is settable to separate positions, and may be set so manually. One position provides power to the branch of the control circuit directed to the right table, an opposite position provides` power to the branch ofthe control circuit directed to theV left table 14, and an intermediate position provides no power to either of these branches. Thus the control circuit is alternatively settable for selecting only that oneof the branches of the circuit which is to control the operation of the selected `workpiecesupportingtable 14 or 15.

The branch for the right table begins with a lead 109 which is connected to a group of electric controls including a normally open momentary start switch 110 thence through the line 111 through a pair of normally open contacts in the left table limit switch, thence through the contacts of ,an overload relay 112, thence through a pair of normally closed contacts in the left table relay 113, and thence to thecoil of a relay 114 for the right table. It will be noted that this circuit can be completed only when the left table is in a fully retracted position so that the normally open contacts of the left limit switch 71 are closed, and if the control relay 113 for the left table is de-energized. Thus, eventhough the right table may have been in its fully retracted position, the limit switch '/'6 does not preclude the starting of the reciprocation thereof. Once the table begins to move, the right limit switch 76 moves to its normal position as shown by the drawing. The establishment of current through the right relay 114, also closes a holding circuit which extends from one contact of the start switch 110, through the now closed or upper contacts in the right limit switch '76, thence through a pair of holding contacts inthe right relay 114 which are now closed, and thence Ato the opposite contacts of the right starting switch 110 whereby current continues to flow through the line 111 subject to the left table holding the appropriate contacts of the left limit switch 71 closed.

The control power line 95 also brings power to a con-V 48, to the right hand solenoid 61 of the valve 49, and to the solenoid of the coolant valve 67. Therefore, if the ett relay 113 is energized or is stuck in an energized position, the contacts thereof which are in series with the coil to the right relay 114 would be open and would prevent energizing of the right table controls.

When the selector switch ismoved to its opposite position, power is brought from the fuse 93 through the line 95, the contacts 107 and the stop switch 108 to a line which leads to the left start switch 115. When the left table start switch 115 is closed, current passes therethrough and to the normally open contacts of the right limit switch 76 which are held in closed position by the retracted position of the right table 15. From the switch the circuit branch extends'through.thecontacts of A.an

Yoverload relay 116. and thence through a pair of contacts v:inthe right relay 114 which are closed if the relay 114 Y 15de-energized. The circuit then eXtendsto the coil of :.theleft relay 113.

- zswitch energizes the coil of the left relay 113 pro- Thus the closing of the left start vided that the right relay 114 is. cie-energized and pro- ;videdt'hat the right table 15 is in its fully retracted position -,The closing of the left relay 113' also closes a hholdingcircuit which extends about the contacts of the .left startswitch 11S, beginning at a point intermediate the switch` 115 and the selector switch y70, extending through the'gnormally closed contacts of the left limit switch 71, which are closed whenever the left vtable is not `its retracted position, and thence extending through the holding contacts of the left relay 113 for communica- `tion with the opposite contacts of thevleft momentary rstart switch 115. Closing of the relay 113 also closes a vcircuit including the contacts shown to be adjacent to the coiloffthe left rrelay which circuit extends through the .-'co'il of theoverload limiting relay 116 and thence to each `of `the solenoidSS of the valve 4S, the solenoid 60 of .the valve 49, and the solenoid coolant valve 66.

In `theevent that current to one of the groups of valves .is excessive, such lcurrent will cause one of the overload limiting relays 112 and 116 to open. -.Accordingly, such relayspreferably are of the manual reset type.

It can be seen that since the normally closed momentarystop switch 10S is in a position ahead of the selector switch 70, a single stop switch through which the control .current passes willserve, upon opening thereof, to injterrupt the current throughthe coil of the left relay 113 as well as through the coil of the rightV relay 114, thereby opening the corresponding holding circuits for such relay.

ThusY itvcan be seen that anl electric control circuit has Fneenprovided `for each table, which is alternatively kselectable .and which includes a plurality of valve sole- Anords, which circuit is in series with a limit switch at the opposite table and in electrical series with the valves .to vvbe controlled, whereby each table must be laterally retractedto close the limit switch for the operation of an opposite table. it is further4 seen that selector means has been provided by which only one motor may be run, which selector means collectively includes a manual selector switch together lwith a plurality of electric valves which are disposedbetween the control means or master valve 24 and the motors 40 and 44. The manual selector switch 70,.,and eachof the relays 113 and 114, as well as each of the limit switches 71 and 76 permit only the `circuit for one `table to be energized at a time. It is 'further seen ythat neither circuit can be energized in this embodimentunless the hydraulic pump motor 19 isalso being energized. It is also seen that each of the overload relays 112 and 116 is disposed in one branch of the circuit respectively, and is responsive to the electric current through the valves in such branch whereby it may move to open the circuit in the event that the current through one'of the valves increases to a predetermined llevel. ,It kis also apparent thateach of the relays 113 and 1,14 is provided witha coil that has associated with it a pair of holding vcontacts for keeping such coil energized, a Vpair ofvnormallyk open contacts which when closed provides power tothe various valves jointly to beenergized for the reciprocation of one table, and also. includes a set of normally closed contacts which are connected in the circuit for the opposite table which contacts open Whenever the coil of the relay is energized to prevent starting ofthe opposite circuit. Further, each of the limit ,swltches ,71 `and 76 is alsoresponsive to tableretraction to break the corresponding holding circuits.

Referring again to Figure 1, it will be noted that there are a series of controls disposed adjacent to the right table 15. YThese include the right start switch 110, the left start switch 115, the stop switch 108, and the se- .lector switch 70. If desired, an emergency master switch 1 17 which .controls the power to the lines .81.-83may motor stop switch 96.

. end of the machine.

.machine tool'10 is a collection of controls generally indicated by the numeral 118 which are used to control table.

secondselector switch 70a connected in parallel or series parallel with the selector switch 70. Because of thesnovel arrangement employed in thecontrol circuit,- the operatorcan still operate only one ofthe tables at a time.

Also located to the left of the machine tool are the i hydraulic pump motor start switch 100 and the hydraulic pump motorl stop switch 101. Adjacent thereto arethe coolant pump motor start switch 97 and the coolant pump Of course, thesecould also be duplicated as already described, if desired, at the opposite Also located at the left end of the the various other controls such as those pertainingto the wheel head motor, .the wheel dresser, and the elevation circuit. l" Y Y To operate the machine,. the hydraulic pump isfiirst started by pushing the startV switch 100, lafter whichthe wheelV motor is started andthen properly positioned by use of the control buttons 118. Next the coolant pump -iss'tarted by pushing the start switch 97. The selector switch 70 is then set for one'table,` suchas the left hand manner which holds the limit switch 76 in an actuated position. This energizes thek solenoids 58, 60,l and solenoid valve 66. The lever 39-1is then engaged, thereby causing the left .hand table to reciprocate v To "operate the right table '15, the selector switch 70 is moved to its oppositie position andtheright hand start switch 1.10 is depressed, after which the lei/ erV 39fmay again be engaged.

In case of mechanical failurelto either table during reciprocation thereof, thelimit switches`71 iand`76'will not permit'energizing of the other table,'..and

wthereby stop all hydraulic pressure arriving'atl either '.table; l f g This invention also provides a novel method" of op-`` erating a machine tool which employs two relatively reciprocable workpiece supporting tables. First, the one workpiece supporting table isrrelatively reciprocatedwith .respect tothe tool supporting means, while the other Workpiece'supporting table is simultaneouslylreadi'ed for future relative reciprocation. This includes such steps as unloading, loading, checking, and the like. Thereafter, the other workpiece supporting table is relatively reciprocated with respect to the tool supporting means and the previously reciprocated workpiece supporting table is simultaneously readied for further relative reciprocation. lt can be seen that this method of operating a machine tool has a distinct advantage in that both the machine and the operator are kept busy substantially all of the time.

Although various minor modifications might be suggested by those versed in the art, it should be understood that I wish to embody within the scope of the patent warranted hereon all such embodiments asreasonably and properly come within the scope of my contribution to the art.

I claim as my invention:

1. ln a machine tool: a tool supporting member; a pair of tables each adapted to support at least one workpiece, and reciprocably disposed adjacent to said member; a pair of motors each operatively connected to one of said tables for reciprocating the same; control means adapted to automatically effect periodically reversing operation of said motors; and selector means operatively disposed intermediate said control means and said pair of Then the left table' start button '1.15 is pushed" providing that the right hand table'15 is at restin a motors by which only one of said pair of motors may be -operated at a single time.

2. In a machine tool: a tool supporting member; a

. pair of tables each adapted to support at least one workpiece, and reciprocably disposed adjacent to said member; a pair of uid motors each operatively connected to one of said tables for reciprocating the same; fluid control means adapted to eiect operation of said' motors, said means being responsive to movement of said tables in either direction to effect operation of said motors in the opposite direction; and manually controllable selector valve means operatively disposed intermediate said fluid control means and said pair of uid motors by which only one of said pair of fluidl motors may be operated at a single time.

3. In a machinetool:v a tool supporting member; a pair ofy tables eachadapted to support at leastoneworkpiece, and reciprocably disposed adjacent to said member; a hydraulic system for reciprocating said tables, said system including a pump, an electric motor for driving ,i said pump, and a plurality ofelectricvalves communieating with said pump for controlling said system; and an electric relay having a coil' connected to be operatively coordinated with said electric motor,'and having contacts Vconnected-for supplying current to Ysaid electric valves only when said coil'is energized.

4. In a machiney tool: a tool supporting member; a pair of/tables each adapted tosupportat leastone workpiece,; and reciprocably disposedl adjacent .to saidmember; a pair of fluidmotors each operatively connected to'oneof Vsaid tables for reciprocating the same; fluid control means adapted to effect operation'of .said motors, said means being responsive,tovmovementof said vtables in either direction to effect operation of ysaid motors in the opposite direction; an electro-fluid control cirwith said `limit'switch'andoperatively intermediate said fluid control means and at least ,one of said vlluidmotors;l

anda selector switch operativeV to energize' only one1-of `said circuits at a time; each l,of said limit switchesbeing p operative to permit operation of itsfcircuit onlyrwhen said opposite table ,is laterally retracted from said tool supporting member. f

5. In a Ymachine tool: a tool supporting-f member; a

. pair o f tables each adapted to support at least one workpiece, and reciprocably disposedadjacent to-said memberta `pair of motorseach operatively connected toone of said tables for reciprocating the same; control means adapted to automatically effect periodically reversing operation of said motors; an electric control circuit for each of said tables, `each of said circuits including a limit switch disposed adjacent to the opposite table; and a selector switch operative to energize only one of said circuits at a time; each of said limit switches being operative to permit operation of its circuit only when said opposite table is laterally retracted from said tool supporting member.

6. In a machine tool: a tool supporting member; a pair of tables each adapted to support at least one work piece, and reciprocably disposed adjacent to said member; a pair of motors each operatively connected to one of said tables for reciprocating the same; control means adapted to automatically etect periodically reversing operation of said motors; an electric control circuit for each of said tables; a selector switch operative to energize only one of said circuits at a time; and means in each of said control circuits responsive to the position of the opposite table to permit operation of its circuit only when said opposite table is laterally retracted from said tool supporting member.

7. In a machine tool: a tool supporting member; a pair of tables each adapted to support at least one workpiece, and reciprocably disposed adjacent to said member;l alpair of-uid motors each operatively `connected to one of said tables for reciprocating the same; iluid control means adapted to effect operation of saidmotors,

said meansbeing responsive to movement of said tables .in either direction to effect operation of saidmotors in .theropposite direction; a iirst selector valve operatively disposed intermediatesaid iluid control meansJ and both of said motors for passing fluidto drive only a selected `one of said motors in a rstdirection; a second selector V`valvefoperatively disposed-intermediate said uid control .means land both offsaid motors for passing uid to drive only said selected motor in an opposite direction;` and vmeans for jointly positioning said valves so that only said selected motor can be operated.

8. In a machine tool: a tool supporting member; a

' pair. of tables each adapted to support at least one Work- Apiece, and reciprocably disposed adjacent to said member; a .pair of uid motors each operatively connected to one of said tables for reciprocating the same; iluid control means adapted to effect operation of -said motors, said means being responsive to movement of said tables in either direction to effect voperation of saidmotors in the opposite direction; a rst selector valve operatively disposed intermediate said uid control means and both ,of` said motors for passing uid tofdrive only aselected one of said motors in a rst direction;` a second selector .i valve operatively disposed intermediate said fluid con- .,trol means and both of said motors for passing uid to drive` only said selected motor in an opposite direction; a

, pair of coolant valves adapted to be connected to a source of coolant and to discharge coolant at each of said tables respectively; and means for jointly positioning said valves so that vonly said selected motor can be operated and so that coolant maybe discharged konly at said table connected thereto.

9. `In amachine tool: a base; a tool supporting member carried by said base; a pair of reciprocable tables disposed adjacent to said member; driving means adapted to move one of said tables only'when the other table is 'in a retracted position, and responsive to said table movement in either direction to effect driving of saidpone table in the opposite direction; and a pair of substantially identical control stations supported by `said base at -V each of the retracted vtable positions, respectively, by each of which the control of either table may be effected.

l0.` In a machine tool: a tool supporting member; a

pair of tables each adapted to support at leastoney wor-lgpiece, and reciprocably disposed ajacent to said member; a uid system for reciprocating said tables, said system `including a plurality of electricv valves for the control :thereof; an alternatively selectable electric control circuit foreachof said tables and including said electric valves, said circuits each being-adapted to position said valves .f jointly so that only one of said tables may be operated respectively; and means in each of said circuits respony sive to the electric current through said valves, and operative to open said circuit upon the increase of said and a pairofnormally closed contacts connected in the .opposite circuit and movable to an open position when said coil is energized, said relay having a pair of normally open contacts connected to energize said valves jointly sothat only the corresponding table may be operated.

12. In a machine tool: a tool supporting member; a

pair ofvtables each adapted. to support at least one Work- 25.

a uid system for reciprocating said tables, said system piece, andgreciprocably disposed adjacent to said member;

including,` a plurality of electric valves for the control thereof; a selector switch settable to separate positions for eiecting individual reciprocation of each of said tables;and a group of electrical controls connected to eachwof said positions, each group including in series a/normallyopen momentary start switch, a normally ,open ,limit` switch disposed to be closed by retraction -of-the opposite table, a relay having a coil connected be operated..A

therein, and a pair of normally closed relay contacts kfrom, the relay of the other group of controls, together ywith a normally closed limit switch disposed to be opened -by retraction of the corresponding table connected in series with a pair of normally open contacts of said relay and jointly connected across said start switch as a holdingA circuit for said-relay coil, said relay having a' pair of normallyfopen contacts connected to. energize said valves jointly so that only the corresponding table may References,I Cited in the lile of this patent VUNITED STATES PATENTS Hyde et al. Jan. 13, 1885 Johnson T June 10, 1958 

